Numerous types of implantable medical workpieces are in common use today. Some of these, such as stents and shunts, are implanted surgically, that is, the operating physician surgically accesses the target site and implants the device by hand. Others, such as embolic and brachytherapy devices are more often attached to the end of a delivery apparatus, which is then directed to the target site, whereupon the device is detached and deposited at the site. An example of such a delivery apparatus is a steerable catheter. The medical workpiece is placed at the distal end of a pusher wire that can be threaded through a lumen in the catheter. The catheter is steered to the target site, the pusher wire, with the workpiece attached, is threaded through the catheter lumen and out into the target site. There, the connection between the implant and the pusher wire is severed, the wire and catheter are withdrawn and the workpiece is implanted.
A great deal of effort has gone into devising ways of effecting the separation of a medical workpiece from the delivery apparatus. Mechanical (U.S. Pat. No. 5,234,437 (unscrews), U.S. Pat. No. 5,250,071 (clasp unhooks), U.S. Pat. No. 5,261,916 (key removed from slot), U.S. Pat. No. 5,304,195 (ball disengages from sleeve), U.S. Pat. No. 5,312,415 (device pushed off guidewire) and U.S. Pat. No. 5,350,397 (ball dislodged from socket)), electrolytic (U.S. Pat. Nos. 5,122,136 and 5,354,295), and vibrational energy (U.S. Pat. Nos. 6,022,369 and 6,346,091 B1 (vibration ruptures connection) means have been disclosed. While each of these is relatively effective, each has its shortcomings. Mechanical means often involve substantial movement of the separating elements possibly resulting in misplacement of the implant. Electrolytic means limit the materials that can be used in the construction of the delivery apparatus, may generate undesirable particulates, are often difficult to control, require a grounding needle inserted in the flesh of the patient and require careful insulation of components to avoid electrolysis at sites other than the desired point of separation. Vibrational force generated at the proximal end of the delivery apparatus must travel to the other end with attendant dissipation of the energy that may affect reliability and also may produce particulate matter when separation occurs.
What is needed is a device/method for separating a medical workpiece from a delivery apparatus that is rapid, reliable, efficient and involves minimum manipulation at the point of separation. The present invention provides such a device and method.